溅射Nb-Ge膜中高TcA15相的形成规律

我们发现高超导转变温度T_c(23K)的溅射Nb-Ge膜,都含有一定量的Nb₅Ge₃相,且Nb/Ge<3。对一般样品,用感应法所测的T_c都低于电阻法所测结果约1—2K,T_c≥22K的量在样品中所占的比例相对来说都比较小。对于只含A15相的薄膜,更显示出具有几个台阶宽的转变曲线,高T_c相含量很少;而对于含有A15相和一定量Nb₅Ge₃相的薄膜,感应法测量结果是一个较陡且光滑的转变曲线。电子显微镜观察呈现出Nb₅Ge₃和A15相的有趣的分布。这些结果对于我们以前提出的Nb₅Ge₃相对高T_cA15相有稳定作用的观点是一个进一步的证明。     

1,2,4,6—四苯基—2—羟基—8—氮杂双环[3、2、1]辛烷的核磁共振研究

用多种核磁共振实验方法并结合其它结构信息,确定1,2,4,6-四苯基-2-羟基8-氮杂双环[3、2、1]辛烷的化学结构,并指定该化合物的核磁共振归属。     

La0.8Ca0.2MnO3/SrTiO3薄膜厚度对其结构及磁学性能的影响

采用多种X射线衍射技术和磁电阻测量技术研究了不同厚度的La_0.8Ca_0.2MnO₃/SrTiO₃ (LCMO/STO)薄膜的应变状态及其对磁电阻性能的影响.结果表明，在STO(001)单晶衬底上生长的LCMO薄膜沿［00l］取向生长.LCMO薄膜具有伪立方钙钛矿结构，随着薄膜厚度的增加，面内晶格参数增加，垂直于面内的晶格参数减小,晶格参数a和b相近，略小于c.LC 关键词： X射线衍射 微结构 应变 物理性能     

低价钛引起的硝基酮还原成环反应

在低价钛(TiCl~4-Zn)试剂作用下,4-硝基酮发生分子内还原成环反应,生成△'-吡咯啉.在同样条件下,4-硝基-1,7-二酮则可反应得到产率较高的8-氮杂双环[3.2.1]辛烷.该化合物具有颠茄生物碱母核结构,从而本文提供了合成这类化合物的新方法.     

Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi

Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La（Fel-xCox）11.9Si1.1 （x=0.04, 0.06, and 0.08） with Curie temperatures of 243 K, 274 K, and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ～230 K to ～320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below Tc, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above Tc. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above Tc, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.     

Investigation the positive moments on the M－T curve of YBCO films measured by using zero-field cooling

The superconducting transition of a YBCO film was measured by a MPMS-5 superconducting quantum interference device magnetometer, using a zero-field cooling process. The experimental results have shown that there are positive magnetic moment and positive peak on the M－T curve. We have proven that these anomalous behaviours are due to measurement error, but not phase transition. We have proposed a simple formula to explain and to calculate quantitatively these anomalous behaviours. It was found that, provided dH>0.59H_p (dH is the inhomogeneous field of the remnant field, H_p is the fully penetrated field of the measured sample), the experimental results will be positive, not negative. If dH≥2H_p, the experimental results will be symmetrical to their real negative values. From the M－T curve, which has positive moment and positive peak below T_c (superconducting transition temperature), we found a new possible method to obtain H_p of the measured sample.     

氧、碳杂质对B1结构氮化钒薄膜的Tc和电阻率ρ(T)的影响

我们对几种典型的溅射B1结构VN_x薄膜进行了T_c和电阻率ρ(T)的测量(从Tconset到300K)。以X-射线衍射术、Auger和XPS技术对这些样品进行了分析。实验结果表明,T_c和ρ(T)随膜的厚度和膜中所含氧、碳等杂质而变化。我们认为,氧在膜中所起的作用可能是阻碍VN_x的B_1结构的形成,造成结构中多空位的情况,压低T_c,并导致电子的跳跃式导电。     

载钯磷酸锆的制备和催化性能研究

本文制备了载钯磷酸锆，作为由丙酮和氢气一步法合成甲基异丁基甲酮（ＭＩＢＫ）的催化剂．考察了制备时的ｐＨ对催化剂比表面积、酸度、酸强度以及催化性能的影响．